The composition, structure and metabolism of the serum lipoproteins in the genetic disorder abetalipoproteinemia are being investigated. Abnormalities in the composition of the apolipoproteins of the high density lipoproteins of these patients suggests that the role of the apolipoproteins as activators of the enzymes involved in lipid metabolism, specifically lecithin-cholesterol acyl transferase (LCAT) and lipoprotein lipase (LPL), may also be abnormal. Implications of these studies for normal lipoprotein metabolism and enzyme activities are being studied. The transport and exchange of tocopherol between plasma lipoproteins and red blood cells are being studied to investigate the controlling factors which may be applied to the exchange of tocopherol between plasma and the tissues. Elevated tocopherol levels are seen in patients with hyperlipoproteinemia; the reasons and possible causes of these observations are being studied. Similar studies are being carried out on another compound, beta-carotene, an agent which has a protective effect against the sunlight-induced skin lesions in patients with the genetic disorder erythropoietic protoporphyria.